The field of this invention is processes for the recovery of hydrocarbons from oil reservoirs.
Tremendous volumes of hydrocarbon liquids remain in-situ in a very large number of oil fields in the United States, even after successful primary, secondary and even tertiary recoveries from such oil fields or reservoirs.
Primary recovery from oil fields or reservoirs involves the conventional means of producing oil, which is either by its own natural well pressure which causes it to flow by itself, or by the use of pumping means at the surface for withdrawing the oil from the reservoir. When the pumping procedure becomes inefficient or impossible, then, in the past, secondary recovery methods have sometimes been employed.
Secondary recovery methods involve the injection of liquids, and also gases in some limited cases, into adjacent wells to the one which is to be produced, with the liquid raising the level of the oil and the bottom hole pressure sufficiently to enable the well to thereafter be produced by pumping so that some additional recovery of the oil can be accomplished. Various liquids are employed, including water, chemically altered water and other chemicals known in the art.
Tertiary recovery methods have also been employed, particularly after the secondary recovery methods have failed to place the well in condition for further recovery. The tertiary recovery methods have employed such means as steam injection, in-situ combustion, and the use of exotic fluid injection methods intended to improve recovery efficiency.
With even the highest recovery efficiency, following the primary and secondary recovery methods, significant amounts of hydrocarbon liquids still remain in oil reservoirs in the United States today, and it has been estimated by competent authorities that average amounts remaining in the wells constitutes almost twice as much oil as has been recovered to date.
Not only has a substantial amount of oil or other hydrocarbons thus been left in the ground in the oil or hydrocarbon reservoirs, but at the same time, another important hydrocarbon, natural gas, has been shipped by pipeline to various parts of the United States. The demand for such natural gas has increased tremendously so that an adequate supply of natural gas for the future appears to be in jeopardy. Further, it is well known that there are peak demands for natural gas, such as occur in the extremely cold winter weather. In the past, efforts have been made to provide underground storage in salt domes and the like for natural gas so that large quantities of gas would be readily available to supply peak demands.
The Applicant is aware of some prior patents which have attempted various techniques for the recovery of hydrocarbons and/or the storage of natural gas, and the differences are noted hereinafter. For example, U.S. Pat. No. 1,067,868 relates to a method of increasing the pressure in a well or reservoir by the use of natural gas injection. This patent was based upon the concept that the gas formed an upper layer in the well formation, similar to that shown in U.S. Pat. No. 3,500,914. In other words, as shown in U.S. Pat. No. 3,500,914, the gas is trapped in a pocket at the upper portion thereof and it was apparently the concept of the patentee in U.S. Pat. No. 1,067,868 that such oil could be forced upwardly by increasing the upper layer of gas. The present invention relates to a relatively flat monoclinal formation, wherein the gas under pressure mixes with the oil and, as will be more fully explained, the light ends of the oil or the liquid hydrocarbon in the well vaporize, and the gas becomes enriched with the liquid hydrocarbon. Also, to some extent the injected gas enters into its liquid phase and intimately mixes with the volume of oil in the reservoir. The well into which the gas is injected causes an increase in the bottom hole pressure of the oil or hydrocarbons in adjacent well or wells so that such well or wells are thereafter capable of being produced, or are produced by their own pressure so that additional oil is removed therefrom.
Examples of secondary and tertiary recovery are found in several prior patents known to the applicant such as U.S. Pat. No. 3,878,891.
U.S. Pat. No. 3,623,552 relates to the injection of a gas such as carbon dioxide, and contrary to the present invention, such patent suggests that methane, which is the primary constituent of pure natural gas which is used in the present invention, is a contaminant.
U.S. Pat. Nos. 2,724,437 and 2,724,438 relate to methods wherein production is obtained from wells that are producing, rather than depleted wells of the type treated with the present invention.
U.S. Pat. No. 3,411,577 relates to the secondary recovery in wells having a trap such as shown in the drawing of U.S. Pat. No. 3,500,914, as indicated by the suggestion in Column 2, line 17, of that patent that the injection of the gas is into the "thinner zone of a reservoir".
In defensive publication, T882013, the recovery of volatile liquid from underground storage is disclosed.
U.S. Pat. No. 2,875,831 relates to dissemination of wetting agents through the strata where the petroleum is located by means of carbonated water, which is a totally different concept from the present invention.
U.S. Pat. No. 2,856,000 discloses the concept of relatively lean high pressure gas increasing the pressure of a low pressure reservoir and also becoming enriched by taking up by retrograde condensation the normally liquid phase hydrocarbons present in the lower pressure condensate reservoir. However, the entire process is kept underground, with two reservoirs, a high pressure zone underlying a low pressure zone, contrary to the present invention, wherein the enriched gas is returned to the surface with the liquid hydrocarbons for the stripping of the gas and the recovery of the hydrocarbons.
U.S. Pat. No. 2,669,307 relates to a typical secondary recovery method wherein water is used to inject into a well for the recovery of oil from one or more other wells in a reservoir.
U.S. Pat. No. 3,123,134 relies upon the repeated pressuring and pressure reduction of gas injected into an oil well for the recovery of oil, which differs from the present invention, wherein the gas pressure is gradually increased over the life of the reservoir, during the reduction of the oil using the method of this invention, until the final native pressure of the reservoir is reached.
Additional patents of interest with respect to underground storage are U.S. Pat. Nos. 3,331,206; 3,807,181; and 3,277,654, all of which are simply related to the storage of gas and do not include the recycling of gas for the recovery of oil from formations, as in the present invention.
U.S. Pat. No. 3,878,891 should also be mentioned as a patent relating to the secondary injection and tertiary injection processes known in the art, utilizing liquids such as water for such production.